Aluminum alloy

ABSTRACT

The present disclosure relates to aluminum alloy including about 1.4% by mass to about 1.6% by mass Mn; about 0.75% by mass to about 2.1% by mass Cu; about 0.4% by mass to about 0.7% by mass Fe; about 0.2% by mass to about 0.5% by mass Mg; about 0.1% by mass to about 0.2% by mass Ti; about 0.03% by mass to about 0.07% by mass Si; and the balance aluminum and incidental impurities. In the aluminum alloy, Al—Mg—Cu compounds are dispersed in a matrix.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2010-074228 filed on Mar. 29, 2010, the disclosure of which including the specification, the drawings, and the claims is hereby incorporated by reference in its entirety.

BACKGROUND

The present disclosure relates to aluminum alloy, and particularly relates to aluminum alloy which can be preferably used for, e.g., automobile body components, and which has high tensile strength, high 0.2% proof stress, and high elongation.

Conventionally, aluminum alloy has been used in, e.g., cylinder heads and cylinder blocks of engines, and gearbox casings for automobiles. Aluminum alloy having various compositions has been proposed in order to improve mechanical properties such as hardness and strength and chemical properties such as a heat resisting property while taking advantage of excellent properties of aluminum, such as a property in which aluminum is light-weight with good workability.

Meanwhile, an approach for realizing improvement of fuel efficiency of vehicles is recently being introduced more than ever. Specifically, technology for using light-weight aluminum alloy in panel components such as roof panels, door panels, and bonnets is being developed. In addition, it has been known that an extruded product made of aluminum alloy is used in frame components such as bumper reinforcements and crash cans, for which energy absorbency is required.

When using aluminum alloy for the vehicle body components, an extruded product or a plate-like member which has high ductility as compared to castings is often used for components for which high tensile strength and high elongation are required. However, a cost of the extruded product or the plate-like member is high, and, e.g., secondary processing and joining are often required. Thus, the use of the extruded product or the plate-like member tends to increase an overall cost. For the foregoing reason, it is required that a component having higher tensile strength and higher elongation is manufactured by a casting method by which a plurality of components can be integrally formed at low cost.

For example, Japanese Patent Publication No. H09-268340 discloses high-ductility aluminum alloy containing Mn of about 0.5-2.5 percent by mass (% by mass); Fe of about 0.1-1.5% by mass; Mg of about 0.01-1.2% by mass; and the balance aluminum and incidental impurities. According to the high-ductility aluminum alloy, in so-called “Al-1.5% Mn alloy,” high tensile strength is ensured while improving both of castability and elongation.

SUMMARY

However, as described in a first example of Japanese Patent Publication No. H09-268340, there is aluminum alloy having low tensile strength (162 (MPa)), and therefore there is a problem in which it is difficult to stably manufacture castings made of aluminum alloy having high tensile strength and high elongation. In order to use such castings having the insufficient tensile strength for vehicle body components, an additional reinforcement member is required, and therefore there is a possibility that the number of manufacturing processes and cost are increased.

The present disclosure has been made in view of the foregoing, and it is an object of the present disclosure to provide a technique for manufacturing aluminum alloy which can be preferably used for, e.g., complex vehicle body components, and which has high tensile strength, high 0.2% proof stress, and high elongation.

In order to solve the foregoing problem, the inventors of the present disclosure have conducted various studies and experiments, and the results show the following finding (a):

(a) So-called “Al-1.5% Mn alloy” contains Cu, and a Cu content is properly adjusted (specifically, the Cu content is adjusted to a range of greater than or equal to about 0.75% by mass and less than or equal to about 2.1% by mass). Thus, Al—Mg—Cu compounds having higher strength can be dispersed in a matrix (primary alpha phase). Consequently, the Al—Mg—Cu compound can improve tensile strength, 0.2% proof stress, and elongation of the Al-1.5% Mn alloy as compared to those of conventional alloy.

Further, in order to ensure ductility of the Al-1.5% Mn alloy, the inventors have studied Al—Fe—Mn compounds which improve the ductility by forming a preferable distribution state of a precipitated phase during casting, and which significantly degrade the ductility if such compounds are formed as coarse crystals. The results show the following finding (b):

(b) The Al-1.5% Mn alloy contains Cu, and a Cu content is properly adjusted. Thus, a secondary phase can be dispersed in clumps in a matrix (primary alpha phase), and the Al—Fe—Mn compounds can be dispersed in the secondary phase in a state in which the Al—Fe—Mn compounds are mixed with Al—Fe—Mn—Cu compounds. In the following description, the primary alpha phase may be simply referred to as a “matrix.”

The aluminum alloy of the present disclosure has been made based on the foregoing findings.

The present disclosure is intended for aluminum alloy of the following (1)-(4):

(1) aluminum alloy including about 1.4% by mass to about 1.6% by mass Mn, about 0.75% by mass to about 2.1% by mass Cu, about 0.4% by mass to about 0.7% by mass Fe, about 0.2% by mass to about 0.5% by mass Mg, about 0.1% by mass to about 0.2% by mass Ti, about 0.03% by mass to about 0.07% by mass Si, and the balance aluminum and incidental impurities; in which Al—Mg—Cu compounds are dispersed in a matrix;

(2) the aluminum alloy of (1), including about 1.0% by mass to about 2.1% by mass Cu;

(3) the aluminum alloy of (1) or (2), in which a secondary phase is dispersed in the matrix; and Al—Fe—Mn compounds are dispersed in the secondary phase; and

(4) the aluminum alloy of any one of (1)-(3), which is casting aluminum alloy.

Note that the “matrix (primary alpha phase)” in the present disclosure means a structural phase having the maximum area ratio in a crystal structural phase forming a metal structure containing aluminum as a base. In addition, the “secondary phase” means a crystal structural phase having the maximum area ratio in the remaining phase (various precipitated phases) other than the matrix (primary alpha phase).

According to the aluminum alloy of the present disclosure, in the Al-1.5% Mn alloy, the Cu content is adjusted to the range of greater than or equal to about 0.75% by mass and less than or equal to about 2.1% by mass. Thus, the Al—Mg—Cu compounds are dispersed in the matrix, and therefore mechanical properties of the Al-1.5% Mn alloy can be stably improved as compared to those of the conventional alloy. This allows manufacturing of aluminum alloy which can be preferably used for, e.g., complex vehicle body components, and which has high tensile strength, high 0.2% proof stress, and high elongation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating a relationship of alloy types with tensile strength, 0.2% proof stress, and elongation.

FIG. 2 is an EPMA compound mapping picture showing an internal state of a test piece used for a test number 4 of examples of the present disclosure.

FIG. 3 is an enlarged optical micrograph showing a matrix of the test piece used for the test number 4 of the examples of the present disclosure.

FIG. 4 is an enlarged optical micrograph showing a matrix of a test piece used for a test number 7 of comparative examples.

FIG. 5 is an enlarged optical micrograph showing a matrix of a test piece used for a test number 8 of the comparative examples.

FIG. 6A is a side view of a product manufactured by casting aluminum alloy into a mold of JIS H5202.

FIG. 6B is an end view of the product manufacture by casting aluminum alloy into the mold of JIS H5202.

DETAILED DESCRIPTION

As described above, aluminum alloy of the present disclosure includes about 1.4% by mass to about 1.6% by mass Mn; about 0.75% by mass to about 2.1% by mass Cu; about 0.4% by mass to about 0.7% by mass Fe; about 0.2% by mass to about 0.5% by mass Mg; about 0.1% by mass to about 0.2% by mass Ti; about 0.03% by mass to about 0.07% by mass Si; and the balance aluminum and incidental impurities. In the aluminum alloy of the present disclosure, Al—Mg—Cu compounds are dispersed in a matrix (primary alpha phase). Reasons why the present disclosure is specified as described above, and preferable ranges will be described below. In the description below, unless otherwise noted, “%” representing a content of a chemical composition means a “% by mass.”

(1) Chemical Compositions

Mn (Manganese): about 1.4% to about 1.6% (Greater than or Equal to about 1.4% and Less than or Equal to about 1.6%)

Mn is an element contributing to reduction or prevention of sticking of molten metal to a mold. In addition, Mn forms an Al—Fe—Mn compound, and improves ductility depending on a fair distribution of the Al—Fe—Mn compounds. In order to ensure such advantages, it is required that the aluminum alloy of the present disclosure contains Mn of greater than or equal to about 1.4%. However, if a Mn content exceeds 1.6%, coarse crystals are generated during casting, thereby reducing elongation. Thus, the Mn content is within the range of greater than or equal to about 1.4% and less than or equal to about 1.6%.

Cu (Copper): about 0.75% to about 2.1% (Greater than or Equal to about 0.75% and Less than or Equal to about 2.1%)

Cu is an essential element for improving tensile strength, 0.2% proof stress, and the elongation of the aluminum alloy of the present disclosure. In order to achieve such an advantage, it is required that the aluminum alloy of the present disclosure contains Cu of greater than or equal to about 0.75%. If the aluminum alloy of the present disclosure contains Cu of greater than or equal to about 1.0%, a further enhanced advantage can be achieved. However, if the aluminum alloy of the present disclosure contains Cu exceeding about 2.1%, the ductility is reduced. Thus, a Cu content is within the range of greater than or equal to about 0.75% and less than or equal to about 2.1%. More preferably, the Cu content is within a range of greater than or equal to about 1.0% and less than or equal to about 2.1%.

Fe (Iron): about 0.4% to about 0.7% (Greater than or Equal to about 0.4% and Less than or Equal to about 0.7%)

Fe has an advantage that the sticking of molten metal to the mold is reduced or prevented when casting. If an Fe content is below about 0.4%, the sticking to the mold is easily caused; whereas, if the Fe content is above 0.7%, coarse crystals are easily generated as in Mn, and the elongation is reduced as compared to conventional alloy. Thus, the Fe content is within the range of greater than or equal to about 0.4% and less than or equal to about 0.7%.

Mg (Magnesium): about 0.2% to about 0.5% (Greater than or Equal to about 0.2% and Less than or Equal to about 0.5%)

Mg coexists with Si, and is precipitated as Mg₂Si by thermal processing. Thus, mechanical strength such as the tensile strength and the proof stress are improved. However, if a Mg content is below about 0.2%, it is less likely to achieve such an advantage; whereas, if the Mg content exceeds about 0.5%, the ductility is reduced. Thus, the Mg content is within the range of greater than or equal to about 0.2% and less than or equal to about 0.5%.

Ti (Titanium): about 0.1% to about 0.2% (Greater than or Equal to about 0.1% and Less than or Equal to about 0.2%)

Ti refines the grain size of cast metal, thereby improving cast metal properties, and reducing or preventing hot tearing. However, if a Ti content is below about 0.1%, it is less likely to achieve such an advantage, and therefore it is difficult to substantially reduce or prevent the hot tearing. On the other hand, if the Ti content is above about 0.2%, coarse compounds are generated, thereby reducing the elongation and molten metal fluidity. Thus, the Ti content is within the range of greater than or equal to about 0.1% and less than or equal to about 0.2%.

Si (Silicon): about 0.03% to about 0.07% (Greater than or Equal to about 0.03% and Less than or Equal to about 0.07%)

Si acts to increase the strength, but it is less likely to achieve such an advantage if a Si content is less than about 0.03%. On the other hand, if the Si content exceeds about 0.07%, Si and Fe together form kinds of intermetallic compounds, i.e., Al—Fe—Si compounds, thereby degrading the ductility. Thus, the lower limit of the Si content is about 0.03%, and the upper limit of the Si content is about 0.07%.

Al (Aluminum) is an element contributing to a reduction in weight of, e.g., automobile components, and therefore Al, the impurities, and other required alloy elements together form the remaining portion.

(2) Al—Mg—Cu Compound

The Al—Mg—Cu compound acts to increase the strength. Thus, the aluminum alloy of the present disclosure contains Cu of greater than or equal to about 0.75%, and therefore the Al—Mg—Cu compounds are actively generated and dispersed in the matrix (primary alpha phase). However, addition of a large amount of Cu may result in reduction in hot tearing. Thus, the Cu content is limited as described above.

(3) Al—Fe—Mn Compound

By controlling the size of the Al—Fe—Mn compound to about 6-15 μm, the Al—Fe—Mn compound improves the ductility. However, if the coarse Al—Fe—Mn compounds having a size of greater than or equal to about 50 μm are formed, the ductility is significantly degraded. In particular, if the total content of Mn and Fe exceeds about 1.3%, the coarse crystals are formed during casting, thereby reducing the ductility. Thus, in the present disclosure, the total content of Mn and Fe is adjusted so that the Al—Fe—Mn compounds are finely dispersed not in the matrix but in a secondary phase. Further, the Cu content is properly adjusted, and therefore the Al—Fe—Mn compounds are dispersed in the secondary phase in a state in which the Al—Fe—Mn compounds are mixed with Al—Fe—Mn—Cu compounds.

In the aluminum alloy of the present disclosure, which is designed as described above, the Cu content is adjusted to the range of greater than or equal to about 0.75% by mass and less than or equal to about 2.1% by mass. Thus, the cast metal having the high tensile strength, the high 0.2% proof stress, and the high elongation can be manufactured by a known casting method such as gravity casting, low-pressure die casting, high-pressure die casting, and squeeze casting.

The present disclosure will be described below in detail with reference to examples, but is not limited to such examples.

EXAMPLES

Various aluminum alloys 1-8 having chemical compositions shown in Table 1 were molten by an electric furnace, and then each aluminum alloy was casted into a mold according to the Japanese Industrial Standard (JIS) H5202 at a molten metal temperature of 740° C. and a mold temperature of 200° C. by a typical mold gravity casting (see FIGS. 6A and 6B).

A tensile test piece according to JIS 14A was cut out from the center of a casted product 1 obtained by the foregoing technique. Then, a tensile test was implemented at a testing rate of 3 mm/min and a room temperature by using an Autograph manufactured by Shimadzu Corporation, and mechanical properties such as tensile strength (MPa), 0.2% proof stress (MPa), and elongation (%) were measured. The results are shown in Table 2 and FIG. 1. The alloys 1-5 in Table 1 are aluminum alloys having chemical compositions falling within the ranges specified in the present disclosure. On the other hand, the alloys 6-8 are aluminum alloys having chemical compositions which do not satisfy the conditions specified in the present disclosure.

TABLE 1 Chemical Composition (% by mass) Alloy Balance Aluminum and Impurities Class Number Mn Si Mg Cu Fe Ti Examples of 1 1.43 0.05 0.24 0.75 0.56 0.15 the Present 2 1.42 0.05 0.24 1.00 0.56 0.15 Disclosure 3 1.41 0.05 0.24 1.26 0.57 0.15 4 1.41 0.05 0.24 1.70 0.55 0.15 5 1.41 0.05 0.24 2.10 0.55 0.15 Comparative 6 1.60 0.05 0.24 *0.00 0.60 0.20 Examples 7 1.45 0.05 0.24 *0.42 0.56 0.15 8 1.40 0.05 0.24 *2.50 0.55 0.15 *A Cu content does not satisfy the conditions specified in the present disclosure.

TABLE 2 0.2% Tensile Proof Test Alloy Strength Stress Elongation Class Number Number (MPa) (MPa) (%) Examples of 1 1 182 90 11.0 the Present 2 2 201 100 12.0 Disclosure 3 3 213 115 12.7 4 4 209 112 14.3 5 5 199 114 10.5 Comparative 6 *6  123 73 11.0 Examples 7 *7  150 85 7.0 8 *8  240 207 6.3 *Alloy does not satisfy conditions specified in the present disclosure.

As will be seen from Table 2, in any of the test numbers 1-5 of the examples of the present disclosure, which use the alloys 1-5 satisfying the conditions specified in the present disclosure, it has been confirmed that the tensile strength is greater than or equal to about 182 (MPa), the 0.2% proof stress is greater than or equal to about 90 (MPa), and the elongation is greater than or equal to about 10.5(%); and therefore the alloys 1-5 have the high mechanical properties. Thus, the tests provide a supportive evidence showing that the aluminum alloy of the present disclosure has sufficient capability of achieving at least the three mechanical properties in practical use.

When observing the alloy 4 used for the test number 4 of the examples of the present disclosure by an EPMA (electron probe microanalyzer) analysis, it has been confirmed that, as illustrated in FIG. 2, a secondary phase is dispersed so as to form in clumps in a matrix, and Al—Fe—Mn compounds and Al—Fe—Mn—Cu compounds are dispersed in the secondary phase in a state in which the Al—Fe—Mn compounds and the Al—Fe—Mn—Cu compounds are mixed with each other. Further, as illustrated in FIG. 3, it has been clearly confirmed that the Al—Mg—Cu compounds are dispersed in the matrix.

On the other hand, in the test numbers 6-8 of the comparative examples using the alloys 6-8 having the Cu content which does not satisfy the conditions specified in the present disclosure, it has been confirmed that, in any of the alloys having the Cu content less than the Cu content specified in the present disclosure (test numbers 6 and 7), and the alloy having the Cu content greater than the Cu content specified in the present disclosure (test number 8), at least one of the mechanical properties, i.e., the tensile strength, the 0.2% proof stress, and the elongation is significantly degraded as compared to those of the examples of the present disclosure.

Specifically, it has been confirmed that, in the test number 6 of the comparative example using the alloy 6 which does not contain Cu, the alloy has the elongation equal or approximately equal to those of the examples of the present disclosure, but the tensile strength and the 0.2% proof stress are significantly degraded as compared to those of the examples of the present disclosure. In addition, it has been confirmed that, in the test number 7 of the comparative example using the alloy 7 having the Cu content less than the Cu content specified in the present disclosure, all of the tensile strength, the 0.2% proof stress, and the elongation are degraded as compared to those of the examples of the present disclosure.

Further, it has been confirmed that, in the test number 8 of the comparative example using the alloy 8 having the Cu content exceeding the Cu content specified in the present disclosure, the tensile strength and the 0.2% proof stress are improved as compared to those of the examples of the present disclosure, but the elongation is significantly degraded as compared to those of the examples of the present disclosure (less than 50% of the values of the test numbers 3 and 4 of the examples of the present disclosure).

When observing the alloy 7 used for the test number 7 of the comparative example by the optical microscope as in the examples of the present disclosure, it has been confirmed that the Al—Mg—Cu compounds are not dispersed in the matrix as illustrated in the enlarged view of FIG. 4.

In addition, when observing the alloy 8 used for the test number 8 of the comparative example by the EPMA analysis as in the examples of the present disclosure, it has been confirmed that, as illustrated in the enlarged view of FIG. 5, the Al—Mg—Cu compounds are not dispersed in the matrix, and coarse spherical Cu containing compounds which are different from the Al—Mg—Cu compound are dispersed. Such spherical Cu containing compounds are not dispersed in the alloy 7, and therefore significantly degrade the elongation (ductility) in the test number 8 of the comparative example. When observing the alloy 6 used for the test number 6 of the comparative example by the optical microscope, it has been confirmed that the Al—Mg—Cu compounds form a most part of the secondary phase.

As described above, even if Al-1.5% Mn alloy is used, which is the same as the alloy of the present disclosure except for the Cu content, the alloys of the comparative examples, the Cu content of which does not satisfy the conditions specified in the present disclosure cannot be used due to problems of reliability relating to, e.g., durability.

As illustrated in FIG. 1, the mechanical properties (in particular, the tensile strength and the elongation) are significantly improved within the Cu content range of greater than or equal to about 0.75% and less than or equal to about 2.1%, and the elongation is significantly improved within the Cu content range of greater than or equal to about 1.0% and less than or equal to about 2.1%. This shows technical values of the claimed ranges of the present disclosure.

As described above, the present disclosure is useful for, e.g., aluminum alloy used for vehicle body and chassis components such as suspension members, pillars, joint members, suspension towers, and crush cans. 

1. Aluminum alloy, comprising: about 1.4% by mass to about 1.6% by mass Mn; about 0.75% by mass to about 2.1% by mass Cu; about 0.4% by mass to about 0.7% by mass Fe; about 0.2% by mass to about 0.5% by mass Mg; about 0.1% by mass to about 0.2% by mass Ti; about 0.03% by mass to about 0.07% by mass Si; and the balance aluminum and incidental impurities, wherein Al—Mg—Cu compounds are dispersed in a matrix.
 2. The aluminum alloy of claim 1, further comprising: about 1.0% by mass to about 2.1% by mass Cu.
 3. The aluminum alloy of claim 1, wherein a secondary phase is dispersed in the matrix; and Al—Fe—Mn compounds are dispersed in the secondary phase.
 4. The aluminum alloy of claim 2, wherein a secondary phase is dispersed in the matrix; and Al—Fe—Mn compounds are dispersed in the secondary phase.
 5. The aluminum alloy of claim 1, wherein the aluminum alloy is casting aluminum alloy.
 6. The aluminum alloy of claim 2, wherein the aluminum alloy is casting aluminum alloy.
 7. The aluminum alloy of claim 3, wherein the aluminum alloy is casting aluminum alloy.
 8. The aluminum alloy of claim 4, wherein the aluminum alloy is casting aluminum alloy. 